U.S. patent application number 12/089054 was filed with the patent office on 2009-10-15 for multiple output switching power source apparatus.
This patent application is currently assigned to Sanken Electric Co., Ltd. Invention is credited to Yoichi Kyono.
Application Number | 20090256423 12/089054 |
Document ID | / |
Family ID | 37906268 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090256423 |
Kind Code |
A1 |
Kyono; Yoichi |
October 15, 2009 |
MULTIPLE OUTPUT SWITCHING POWER SOURCE APPARATUS
Abstract
A multiple output switching power source apparatus includes
first and second switching elements Q1 and Q2, a first series
resonant circuit connected in parallel with Q1 or Q2 and having a
first current resonant capacitor and a primary winding of a
transformer that are connected in series, a first
rectifying-smoothing circuit to rectify and smooth a voltage
generated by a secondary winding of the transformer, a second
series resonant circuit connected in parallel with the secondary
winding and having a second current resonant capacitor and a second
resonant reactor that are connected in series, a second
rectifying-smoothing circuit to rectify and smooth a voltage of the
second series resonant circuit, and a control circuit to determine
an ON period of Q1 according to a voltage obtained from one of the
first and second rectifying-smoothing circuits, determine an ON
period of Q2 according to a voltage obtained from the other of the
first and second rectifying-smoothing circuits, and alternately
turn on/off Q1 and Q2.
Inventors: |
Kyono; Yoichi; (Saitama,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Sanken Electric Co., Ltd
Saitama
JP
|
Family ID: |
37906268 |
Appl. No.: |
12/089054 |
Filed: |
October 3, 2006 |
PCT Filed: |
October 3, 2006 |
PCT NO: |
PCT/JP2006/319794 |
371 Date: |
April 3, 2008 |
Current U.S.
Class: |
307/31 |
Current CPC
Class: |
H02M 3/33561 20130101;
Y02B 70/10 20130101 |
Class at
Publication: |
307/31 |
International
Class: |
H02J 1/00 20060101
H02J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 3, 2005 |
JP |
2005 289934 |
Feb 21, 2006 |
JP |
2006 044321 |
Claims
1. A multiple output switching power source apparatus comprising: a
first switching element and a second switching element being
connected in series between output terminals of a DC power source;
a first series resonant circuit connected in parallel with the
first switching element or the second switching element and having
a first current resonant capacitor, a first resonant reactor, and a
primary winding of a transformer those are connected in series; a
first rectifying-smoothing circuit configured to rectify and smooth
a voltage generated by a secondary winding of the transformer; a
second series resonant circuit connected in parallel with the
secondary winding of the transformer and having a second current
resonant capacitor and a second resonant reactor those are
connected in series; a second rectifying-smoothing circuit
configured to rectify and smooth a voltage of the second series
resonant circuit; and a control circuit configured to determine an
ON period of the first switching element according to a voltage
obtained from any one of the first rectifying-smoothing circuit and
second rectifying-smoothing circuit, determine an ON period of the
second switching element according to a voltage obtained from the
other of the first rectifying-smoothing circuit and second
rectifying-smoothing circuit, and alternately turn on/off the first
switching element and second switching element.
2. The multiple output switching power source apparatus as set
forth in claim 1, wherein: the secondary winding of the transformer
has a first secondary winding and a second secondary winding; the
first rectifying-smoothing circuit rectifies and smoothes a voltage
generated by the first secondary winding of the transformer; and
the second series resonant circuit is connected in parallel with
the second secondary winding.
3. The multiple output switching power source apparatus as set
forth in claim 2, wherein the first secondary winding and second
secondary winding of the transformer are loosely coupled with each
other.
4. The multiple output switching power source apparatus as set
forth in claim 1, wherein a first reactor is arranged in a line
extending along the second series resonant circuit and the second
rectifying-smoothing circuit.
5. The multiple output switching power source apparatus as set
forth in claim 1, further comprising a second transformer having a
primary winding and a secondary winding, the second resonant
reactor of the second series resonant circuit having the primary
winding of the second transformer, the second rectifying-smoothing
circuit rectifying and smoothing a voltage generated by the
secondary winding of the second transformer.
6. The multiple output switching power source apparatus as set
forth in claim 5, wherein the primary winding and secondary winding
of the second transformer are loosely coupled with each other.
7. The multiple output switching power source apparatus as set
forth in claim 1, further comprising a second transformer having a
plurality of secondary windings, the second reactor being included
in a primary winding of the second transformer, wherein the second
rectifying-smoothing circuit rectifies and smoothes voltages
generated by the plurality of secondary windings of the second
transformer.
8. The multiple output switching power source apparatus as set
forth in claim 7, wherein: the secondary winding of the first
transformer has a first secondary winding and a second secondary
winding; the first rectifying-smoothing circuit rectifies and
smoothes a voltage generated by the first secondary winding of the
first transformer; and the second series resonant circuit is
connected in parallel with the second secondary winding of the
first transformer.
9. The multiple output switching power source apparatus as set
forth in claim 7, wherein: the plurality of secondary windings of
the second transformer include a first secondary winding and a
second secondary winding being connected in series with the first
secondary winding; and the second rectifying-smoothing circuit has
a smoothing capacitor whose first end is connected to a connection
point of a first end of the first secondary winding and a first end
of the second secondary winding, a first diode connected to a
second end of the first secondary winding and a second end of the
smoothing capacitor, and a second diode connected to a second end
of the second secondary winding and the second end of the smoothing
capacitor.
10. A multiple output switching power source apparatus comprising:
a first switching element and a second switching element being
connected in series between output terminals of a DC power source;
a first series resonant circuit having a first current resonant
capacitor, a first resonant reactor, and a primary winding of a
first transformer those being connected in series, the first series
resonant circuit being connected in parallel with the first
switching element or the second switching element; a second series
resonant circuit having a second current resonant capacitor, a
second resonant reactor, and a primary winding of a second
transformer those being connected in series, the second series
resonant circuit being connected in parallel with the first series
resonant circuit; a first rectifying-smoothing circuit configured
to rectify and smooth a voltage generated by a secondary winding of
the first transformer; a second rectifying-smoothing circuit
configured to rectify and smooth a voltage generated by a secondary
winding of the second transformer; and a control circuit configured
to determine an ON period of the first switching element according
to a voltage obtained from any one of the first
rectifying-smoothing circuit and second rectifying-smoothing
circuit, determine an ON period of the second switching element
according to a voltage obtained from the other of the first
rectifying-smoothing circuit and second rectifying-smoothing
circuit, and alternately turn on/off the first switching element
and second switching element.
11. The multiple output switching power source apparatus as set
forth in claim 10, wherein the second series resonant circuit is
connected in parallel with a series circuit including the first
resonant reactor and the primary winding of the first
transformer.
12. The multiple output switching power source apparatus as set
forth in claim 10, wherein the first resonant reactor and second
resonant reactor are leakage inductances of the first transformer
and second transformer, respectively.
13. The multiple output switching power source apparatus as set
forth in claim 10, wherein: the secondary winding of the first
transformer is wound in a direction in a manner as to generate a
voltage to be rectified by the first rectifying-smoothing circuit
in an ON period of one of the first switching element and second
switching element; and the secondary winding of the second
transformer is wound in a direction in a manner as to generate a
voltage to be rectified by the second rectifying-smoothing circuit
in an ON period of the other of the first switching element and
second switching element.
14. The multiple output switching power source apparatus as set
forth in claim 10, wherein: the secondary winding of the first
transformer is wound in a direction in a manner as to generate a
voltage to be rectified by the first rectifying-smoothing circuit
in an ON period of one of the first switching element and second
switching element; and the secondary winding of the second
transformer is wound in a direction in a manner as to generate a
voltage to be rectified by the second rectifying-smoothing circuit
in the ON period.
Description
TECHNICAL FIELD
[0001] The present invention relates to a multiple output switching
power source apparatus having a plurality of outputs.
BACKGROUND TECHNOLOGY
[0002] FIG. 1 is a circuit diagram illustrating the configuration
of a resonant-type multiple output switching power source apparatus
according to a related art. In this multiple output switching power
source apparatus, the primary side of a transformer T1 includes a
full-wave rectifying circuit 2 to rectify an AC voltage from a
commercial power source 1, a smoothing capacitor C3 connected
between output terminals of the full-wave rectifying circuit 2, to
smooth an output from the full-wave rectifying circuit 2, a first
switching element Q1 and a second switching element Q2 (for
example, MOSFETs) that are connected in series between ends of the
smoothing capacitor C3, to receive a terminal voltage of the
smoothing capacitor C3 as a DC input voltage sin, a control circuit
10 to control ON/OFF of the first switching element Q1 and second
switching element Q2, a voltage resonant capacitor Crv connected in
parallel with the second switching element Q2, and a series
resonant circuit connected to both ends of the voltage resonant
capacitor Crv.
[0003] The series resonant circuit consists of a primary winding P1
(the number of turns of N1) of the transformer T1, a reactor Lr,
and a current resonant capacitor Cri that are connected in series.
The reactor Lr is, for example, a leakage inductance between the
primary and secondary sides of the transformer T1.
[0004] On the secondary side of the transformer T1, a first
secondary winding S1 (the number of turns of N2) is wound to
generate a voltage whose phase is opposite to the phase of a
voltage of the primary winding P1 of the transformer T1, a first
rectifying-smoothing circuit is connected to the first secondary
winding S1, a second secondary winding S2 (the number of turns of
N3) is wound to generate a voltage whose phase is opposite to the
phase of the voltage of the primary winding P1 of the transformer
T1, and a second rectifying-smoothing circuit is connected to the
second secondary winding S2.
[0005] The first rectifying-smoothing circuit has a diode D1 and a
smoothing capacitor C1, rectifies and smoothes a voltage induced by
the first secondary winding S1 of the transformer T1, and outputs a
first output voltage Vo1 from a first output terminal. The second
rectifying-smoothing circuit has a diode D2 and a smoothing
capacitor C2, rectifies and smoothes a voltage induced by the
second secondary winding S2 of the transformer T1, and outputs a
second output voltage Vo2 from a second output terminal.
[0006] This multiple output switching power source apparatus has a
feedback circuit 5 to feed back to the primary side a signal
corresponding to a voltage generated on the secondary side of the
transformer T1. Namely, an input side of the feedback circuit 5 is
connected to the first output terminal (Vo1), compares a terminal
voltage of the smoothing capacitor C1 with a predetermined
reference voltage, and feeds an error voltage as a voltage error
signal back to the control circuit 10 on the primary side.
[0007] According to the voltage error signal fed back from the
feedback circuit 5, the control circuit 10 alternately turns on/off
the first switching element Q1 and second switching element Q2
thereby carrying out PWM control of controlling the first output
voltage Vo1 to be constant. In this case, gates of the first
switching element Q1 and second switching element Q2 receive
control signals, i.e., voltages that may set a dead time of about
several hundreds of nanoseconds. With this, the first switching
element Q1 and second switching element Q2 do not overlap their ON
periods with each other and are alternately turned on/off.
[0008] Operation of the multiple output switching power source
apparatus according to the related art having the above-mentioned
configuration will be explained with reference to waveforms
illustrated in FIG. 2.
[0009] In FIG. 2, VQ2ds is a drain-source voltage of the second
switching element Q2, IQ1 a current passing through a drain of the
first switching element Q1, IQ2 a current passing through a drain
of the second switching element Q2, Icri a current passing through
the current resonance capacitor Cri, Vcri a terminal voltage of the
current resonant capacitor Cri, ID1 a current passing through the
diode D1, VN2 a terminal voltage of the first secondary winding S1,
and ID2 a current passing through the diode D2.
[0010] The first output voltage Vo1 is controlled by the control
circuit 10 that receives the voltage error signal fed back to the
primary side from the first rectifying-smoothing circuit through
the feedback circuit 5 and carries out PWM control on the first
switching element Q1. In this case, the first switching element Q1
and second switching element Q2 are alternately turned on/off with
a dead time of about several hundreds of nanoseconds in response to
control signals from the control circuit 10, as mentioned
above.
[0011] First, in an ON period (for example, time t11 to t12) of the
first switching element Q1, the current resonant capacitor Cri
accumulates energy through an exciting inductance of the primary
winding P1 of the transformer T1 and the reactor Lr (leakage
inductance between the primary and secondary sides of the
transformer T1).
[0012] Next, in an ON period (for example, time t12 to t14) of the
second switching element Q2, the energy accumulated in the current
resonant capacitor Cri causes the reactor Lr and current resonant
capacitor Cri to pass a resonant current and send energy to the
secondary side. Also, the exciting energy of the exciting
inductance of the primary winding P1 is reset
[0013] More precisely, in the ON period of the second switching
element Q2, the primary winding P1 receives a voltage that is
produced by dividing the terminal voltage Vcri of the current
resonant capacitor Cri with the exciting inductance of the primary
winding P1 and the reactor Lr. When the voltage applied to the
primary winding P1 reaches (Vo1+Vf).times.N1/N2, it is clamped and
the current resonant capacitor Cri and reactor Lr pass a resonant
current to send energy to the secondary side. This results in
passing the current ID to the diode D1. If the voltage of the
primary winding P1 is smaller than (Vo1+Vf).times.N1/N2, no energy
is transmitted to the secondary side of the transformer T1 and the
exciting inductance of the primary winding P1 of the transformer
T1, the reactor Lr, and the current resonant capacitor Cri conduct
a resonant operation only on the primary side. Here, Vf is a
forward voltage drop of the diode.
[0014] In general, the ON period of the second switching element Q2
is determined by the ON period of the first switching element Q1
under a fixed frequency, or it is an optional fixed period.
Changing the ON period of the first switching element Q1 to change
the duty ratios of the first switching element Q1 and second
switching element Q2 results in changing the voltage of the current
resonant capacitor Cri, and therefore, it is possible to control
the quantity of energy to be sent to the secondary side.
[0015] The first secondary winding S1 and second secondary winding
S2 are coupled with the same polarities. Due to this, while energy
provided by the first secondary winding S1 is being output as the
first output voltage Vo1 in an ON period of the second switching
element Q2, energy provided by the second secondary winding S2 is
output as the second output voltage Vo2. This second output voltage
Vo2 is nearly equal to Vo1.times.N3/N2.
DISCLOSURE OF INVENTION
[0016] However, in practice, the voltages generated by the first
secondary winding S1 and second secondary winding S2 are higher
than the first output voltage Vo1 and second output voltage Vo2 by
the forward voltage drops Vf of the diode D1 and diode D2. As a
result, a change in Vf due to a load variation at each output may
deteriorate a cross regulation. In the case of a power source
apparatus that is designed to vary output voltages, changing one
output voltage results in causing a proportional change in the
other output. Then, it will be impossible to directly take a
plurality of outputs from windings.
[0017] FIG. 3 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
another related art. This multiple output switching power source
apparatus employs, instead of the second rectifying-smoothing
circuit illustrated in FIG. 1, a regulator 12 such as a dropper and
a step-down chopper. The regulator 12 is used to generate a second
output voltage Vo2 from a first output voltage Vo1 so that the
outputs are stabilized. This multiple output switching power source
apparatus can solve the cross regulation problem related to two
outputs. However, the regulator 12 increases a loss, the additional
parts including switching elements, choke coils, control ICs, and
the like increase the cost and a packaging space, and the switching
regulator such as a step-down chopper causes noise.
[0018] As a multiple output switching power source apparatus,
Japanese Unexamined Patent Application Publication No. 2003-259644
discloses a switching converter circuit with one converter
stabilizing two kinds of voltage. This switching converter circuit
arranges a second switching element as an active snubber, controls
ON/OFF of a first switching element to stabilize a first output,
and in an OFF period of the first switching element, controls
ON/OFF of the second switching element to stabilize a second
output. This switching converter circuit can stabilize two kinds of
output with one converter. However, a secondary winding to provide
the first output and a secondary winding to provide the second
output must have opposite polarities. Namely, two secondary
windings are needed.
[0019] As mentioned above, the multiple output switching power
source apparatuses according to the related arts have the problem
of worsening a cross regulation due to load variations at each
output and the problem of not directly taking a plurality of
outputs from windings in the case of the power source designed to
provide variable output voltages. The technique of arranging a
regulator on the secondary side to solve the problem of cross
regulation worsens a loss due to the regulator, increases the cost
and a packaging space due to additional parts, and causes noise due
to the regulator. The switching converter circuit disclosed in the
above related art needs a plurality of secondary windings for a
transformer, to thereby cause a problem of complicating the
structure.
Means to Solve the Problems
[0020] The present invention can provide a multiple output
switching power source apparatus capable of stabilizing a plurality
of outputs even if there are load variations.
[0021] According to a first technical aspect of the present
invention, a multiple output switching power source apparatus
includes a first switching element and a second switching element
that are connected in series between output terminals of a DC power
source, a first series resonant circuit connected in parallel with
the first switching element or the second switching element and
having a first current resonant capacitor, a first resonant
reactor, and a primary winding of a transformer that are connected
in series, a first rectifying-smoothing circuit to rectify and
smooth a voltage generated by a secondary winding of the
transformer, a second series resonant circuit connected in parallel
with the secondary winding of the transformer and having a second
current resonant capacitor and a second resonant reactor that are
connected in series, a second rectifying-smoothing circuit to
rectify and smooth a voltage of the second series resonant circuit,
and a control circuit to determine an ON period of the first
switching element according to a voltage obtained from any one of
the first rectifying-smoothing circuit and second
rectifying-smoothing circuit, determine an ON period of the second
switching element according to a voltage obtained from the other of
the first rectifying-smoothing circuit and second
rectifying-smoothing circuit, and alternately turn on/off the first
switching element and second switching element.
[0022] According to a second technical aspect of the present
invention, the multiple output switching power source apparatus is
further characterized in that the secondary winding of the
transformer has a first secondary winding and a second secondary
winding, the first rectifying-smoothing circuit rectifies and
smoothes a voltage generated by the first secondary winding of the
transformer, and the second series resonant circuit is connected in
parallel with the second secondary winding.
[0023] According to a third technical aspect of the present
invention, the multiple output switching power source apparatus is
further characterized in that the first secondary winding and
second secondary winding of the transformer are loosely coupled
with each other.
[0024] According to a fourth technical aspect of the present
invention, the multiple output switching power source apparatus
includes, in addition to the first technical aspect, a second
transformer having a primary winding and a secondary winding. The
second resonant reactor of the second series resonant circuit has
the primary winding of the second transformer and the second
rectifying-smoothing circuit rectifies and smoothes a voltage
generated by the secondary winding of the second transformer.
[0025] According to a fifth technical aspect of the present
invention, the multiple output switching power source apparatus
includes, in addition to the first technical aspect, a second
transformer having a plurality of secondary windings. The second
reactor is included in a primary winding of the second transformer
and the second rectifying-smoothing circuit rectifies and smoothes
voltages generated by the plurality of secondary windings of the
second transformer.
[0026] According to a sixth technical aspect of the present
invention, the secondary winding of the first transformer has a
first secondary winding and a second secondary winding, the first
rectifying-smoothing circuit rectifies and smoothes a voltage
generated by the first secondary winding of the first transformer,
and the second series resonant circuit is connected in parallel
with the second secondary winding of the first transformer.
[0027] According to a seventh technical aspect of the present
invention, a multiple output switching power source apparatus
includes a first switching element and a second switching element
that are connected in series between output terminals of a DC power
source, a first series resonant circuit in which a first current
resonant capacitor, a first resonant reactor, and a primary winding
of a first transformer are connected in series and which is
connected in parallel with the first switching element or the
second switching element, a second series resonant circuit in which
a second current resonant capacitor, a second resonant reactor, and
a primary winding of a second transformer are connected in series
and which is connected in parallel with the first series resonant
circuit, a first rectifying-smoothing circuit to rectify and smooth
a voltage generated by a secondary winding of the first
transformer, a second rectifying-smoothing circuit to rectify and
smooth a voltage generated by a secondary winding of the second
transformer, and a control circuit to determine an ON period of the
first switching element according to a voltage obtained from any
one of the first rectifying-smoothing circuit and second
rectifying-smoothing circuit, determine an ON period of the second
switching element according to a voltage obtained from the other of
the first rectifying-smoothing circuit and second
rectifying-smoothing circuit, and alternately turn on/off the first
switching element and second switching element.
BRIEF DESCRIPTION OF DRAWINGS
[0028] FIG. 1 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
a related art.
[0029] FIG. 2 is a waveform diagram illustrating operation of the
multiple output switching power source apparatus according to the
related art.
[0030] FIG. 3 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
another related art.
[0031] FIG. 4 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 1 of the present invention.
[0032] FIG. 5 is a waveform diagram illustrating operation of the
multiple output switching power source apparatus according to the
embodiment 1 of the present invention.
[0033] FIG. 6 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 2 of the present invention.
[0034] FIG. 7 is a waveform diagram illustrating operation of the
multiple output switching power source apparatus according to the
embodiment 2 of the present invention.
[0035] FIG. 8 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 3 of the present invention.
[0036] FIG. 9 is a waveform diagram illustrting operation of the
multiple output switching power source apparatus according to the
embodiment 3 of the present invention.
[0037] FIG. 10 is a waveform diagram illustrating operation of a
modification of the multiple output switching power source
apparatus according to the embodiment 3 of the present
invention.
[0038] FIG. 11 is a view illustrating the structure of a
transformer used in the modification of the multiple output
switching power source apparatus according to the embodiment 3 of
the present invention.
[0039] FIG. 12 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 4 of the present invention.
[0040] FIG. 13 is a waveform diagram illustrating operation of the
multiple output switching power source apparatus according to the
embodiment 4 of the present invention.
[0041] FIG. 14 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 5 of the present invention.
[0042] FIG. 15 is a waveform diagram illustrting operation of the
multiple output switching power source apparatus according to the
embodiment 5 of the present invention.
[0043] FIG. 16 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 6 of the present invention.
[0044] FIG. 17 is a waveform diagram illustrting operation of the
multiple output switching power source apparatus according to the
embodiment 6 of the present invention.
[0045] FIG. 18 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 7 of the present invention.
[0046] FIG. 19 is a waveform diagram illustrating operation under
heavy load of the multiple output switching power source apparatus
according to the embodiment 7 of the present invention.
[0047] FIG. 20 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 8 of the present invention.
[0048] FIG. 21 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 9 of the present invention.
[0049] FIG. 22 is a waveform diagram illustrating operation under
heavy load of the multiple output switching power source apparatus
according to the embodiment 9 of the present invention.
[0050] FIG. 23 is a waveform diagram illustrating operation under
light load of the multiple output switching power source apparatus
according to the embodiment 9 of the present invention.
[0051] FIG. 24 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 10 of the present invention.
[0052] FIG. 25 is a waveform diagram illustrating operation under
heavy load of the multiple output switching power source apparatus
according to the embodiment 10 of the present invention.
[0053] FIG. 26 is a waveform diagram illustrating operation under
light load of the multiple output switching power source apparatus
according to the embodiment 10 of the present invention.
[0054] FIG. 27 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
an embodiment 11 of the present invention.
[0055] FIG. 28 is a waveform diagram illustrating operation of the
multiple output switching power source apparatus according to the
embodiment 11 of the present invention.
BEST MODE OF IMPLEMENTING INVENTION
[0056] Multiple output switching power source apparatuses according
to embodiments of the present invention will be explained in detail
with reference to the drawings. In the following explanation, the
same or corresponding parts as those of the multiple output
switching power source apparatus explained in "BACKGROUND
TECHNOLOGY" will be represented with the same reference marks as
those used therein.
Embodiment 1
[0057] FIG. 4 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 1 of the present invention. In this multiple output
switching power source apparatus, the primary side of a transformer
T1 includes a full-wave rectifying circuit 2 to rectify an AC
voltage from a commercial power source 1, a smoothing capacitor C3
connected between output terminals of the full-wave rectifying
circuit 2, to smooth an output from the full-wave rectifying
circuit 2, a first switching element Q1 and a second switching
element Q2 that are connected in series between both ends of the
smoothing capacitor C3, to receive a terminal voltage of the
smoothing capacitor C3 as a DC input voltage Vin, a control circuit
10a to control ON/OFF of the first switching element Q1 and second
switching element Q2, a voltage resonant capacitor Crv connected in
parallel with the second switching element Q2, and a first series
resonant circuit connected to both ends of the voltage resonant
capacitor Crv. The first switching element Q1 and second switching
element Q2 are, for example, MOSFETs.
[0058] The first series resonant circuit has a primary winding P1
(the number of turns of N1) of the transformer T1, a first resonant
reactor Lr, and a first current resonant capacitor Cri those are
connected in series. The first resonant reactor Lr is, for example,
a leakage inductance between the primary and secondary sides of the
transformer T1.
[0059] On the secondary side of the transformer T1, a first
rectifying-smoothing circuit is connected to a secondary winding S1
(the number of turns of N2) that is wound to generate a voltage
whose phase is opposite to the phase of a voltage of the primary
winding P1 of the transformer T1, a second series resonant circuit
is connected in parallel with the secondary winding S1, and a
second rectifying-smoothing circuit is connected to the second
series resonant circuit.
[0060] The first rectifying-smoothing circuit has a diode D1 and a
smoothing capacitor C1. An anode of the diode D1 is connected to a
first end of the secondary winding S1 and a cathode thereof is
connected to a first output terminal. The smoothing capacitor C1 is
connected between the cathode of the diode Di (the first output
terminal) and a second end of the secondary winding S1 (a ground
terminal). The first rectifying-smoothing circuit rectifies and
smoothes a voltage induced by the secondary winding S1 of the
transformer T1 and outputs a first output voltage Vo1 from the
first output terminal.
[0061] The second series resonant circuit has a second current
resonant capacitor Cri2 whose first end is connected to the first
end of the secondary winding S1 (the anode of the diode D1) and a
second resonant reactor Lr2 connected between a second end of the
second current resonant capacitor Cri2 and the second end of the
secondary winding S1 (the ground terminal).
[0062] The second rectifying-smoothing circuit has a diode D2 and a
smoothing capacitor C2. An anode of the diode D2 is connected to a
connection point of the second resonant reactor Lr2 and second
current resonant capacitor Cri2 and a cathode thereof is connected
to a second output terminal. The smoothing capacitor C2 is
connected between the cathode of the diode D2 (the second output
terminal) and the second end of the secondary winding S1 (the
ground terminal). The second rectifying-smoothing circuit rectifies
and smoothes a voltage that is the sum of a voltage generated by
the secondary winding S1 of the transformer T1 and a terminal
voltage of the second current resonant capacitor Cri2 and outputs a
second output voltage Vo2 from the second output terminal.
[0063] This multiple output switching power source apparatus has a
feedback circuit 5 and a feedback circuit 6, to feed voltages
generated on the secondary side of the transformer T1 back to the
primary side. The feedback circuit 5 compares the first output
voltage Vo1 output to the first output terminal with a
predetermined reference voltage and feeds an error voltage as a
first voltage error signal back to the control circuit 10a on the
primary side. The feedback circuit 6 compares the second output
voltage Vo2 output to the second output terminal with a
predetermined reference voltage and feeds an error voltage as a
second voltage error signal back to the control circuit 10a on the
primary side.
[0064] Based on the first voltage error signal from the feedback
circuit 5 and the second voltage error signal from the feedback
circuit 6, the control circuit 10a alternately turns on/off the
first switching element Q1 and second switching element Q2, to
carry out PWM control so that the first output voltage Vo1 and
second output voltage Vo2 remain constant. In this case, gates of
the first switching element Q1 and second switching element Q2
receive voltages as control signals that create a dead time of
about several hundreds of nanoseconds. As a result, the first
switching element Q1 and second switching element Q2 alternately
turn on/off without overlapping their ON periods with each
other.
[0065] Next, operation of the multiple output switching power
source apparatus according to the embodiment 1 of the present
invention having the above-mentioned configuration will be
explained with reference to waveforms illustrated in FIG. 5.
[0066] In FIG. 5, VQ2ds is a drain-source voltage of the second
switching element Q2, IQ1 a current passing through a drain of the
first switching element Q1, IQ2 a current passing through a drain
of the second switching element Q2, Icri a current passing to the
first current resonant capacitor Cri, Vcri a terminal voltage of
the first current resonant capacitor Cri, ID1 a current passing
through the diode D1, VN2 a terminal voltage of the secondary
winding S1, Vcir2 a terminal voltage of the second current resonant
capacitor Cri2, VLr2 a terminal voltage of the second resonant
reactor Lr2, and ID2 a current passing to the diode D2.
[0067] Control of the first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling duties of the first switching element Q1 and
second switching element Q2. Namely, by changing ON-period duty
ratios of the first switching element Q1 and second switching
element Q2, a voltage stored in the first current resonant
capacitor Cri during an ON period of the first switching element Q1
is adjusted, and in an ON period of the second switching element
Q2, energy accumulated in the first current resonant capacitor Cri
makes the first resonant reactor Lr and first current resonant
capacitor Cri resonate. As a result, a resonant current passes to
transmit energy to the secondary side of the transformer T1, and
therefore, it is possible to control the energy to be transmitted
to the secondary side. A voltage generated by the secondary winding
S1 is rectified and smoothed by the first rectifying-smoothing
circuit having the diode D1 and smoothing capacitor C1, to output
the first output voltage Vo1 from the first output terminal.
[0068] Control of the second output voltage Vo2 will be explained.
In an ON period (for example, time t1 to t2) of the first switching
element Q1, a differential voltage between an input voltage Vin and
a terminal voltage of the first current resonant capacitor Cri is
applied to the primary winding P1, and therefore, the secondary
winding S1 generates a voltage that is the differential voltage
multiplied by a turn ratio. The voltage generated by the secondary
winding S1 is applied to the second series resonant circuit having
the second current resonant capacitor Cri2 and second resonant
reactor Lr2, so that the second series resonant circuit resonates
to gradually charge the second current resonant capacitor Cri2.
[0069] In an ON period (for example, time t2 to t4) of the second
switching element Q2, a voltage obtained by adding a voltage
corresponding to energy accumulated in the second current resonant
capacitor Cri2 to a voltage generated by the secondary winding S1
is rectified and smoothed through the second rectifying-smoothing
circuit having the diode D2 and smoothing capacitor C2, to output
the second output voltage Vo2 from the second output terminal. At
this time, the second current resonant capacitor Cri2 is discharged
to reduce the voltage corresponding to the accumulated energy, and
thereafter, is charged by a current in a reverse direction due to
the voltage of the secondary winding S1. When the charging of the
smoothing capacitor C2 ends, the diode D2 passes no current and the
second current resonant capacitor Cri2 gradually discharges due to
a resonant operation with the second resonant reactor Lr2 and is
then charged by a current in a reverse direction. During this
operation, the second switching element Q2 turns off and the first
switching element Q1 turns on, so that the secondary winding S1
reversely induces a voltage and the discharging and reverse
charging operations continue.
[0070] In this way, the second current resonant capacitor Cri2
discharges only during a period in which the second switching
element Q2 turns on to charge the smoothing capacitor C2 and is
charged during the remaining ON period of the second switching
element Q2 and an ON period of the first switching element Q1.
Namely, except the period of charging the smoothing capacitor C2,
it is charged in most of a switching period of the first switching
element Q1 and second switching element Q2. Namely, by changing the
switching period, i.e., switching frequency of the first switching
element Q1 and second switching element Q2, it is possible to
adjust a charging period of the second current resonant capacitor
Cri2 and thereby control the second output voltage Vo2.
[0071] More precisely, according to the second output voltage error
signal provided by the feedback circuit 6, an ON period of the
second switching element Q2 is controlled, and according to the
first output voltage error signal provided by the feedback circuit
5, an ON period of the first switching element Q1 is controlled, to
adjust duties of the first switching element Q1 and second
switching element Q2. Namely, the first output voltage error signal
determines duties and adjusts the first output voltage, and
therefore, controlling an ON period of the second switching element
according to the second output voltage error signal results in
changing a switching frequency and adjusting the second output
voltage.
[0072] The above-mentioned multiple output switching power source
apparatus according to the embodiment 1 controls an ON period of
the second switching element Q2 with the second voltage error
signal based on the second output voltage Vo2 and controls an ON
period of the first switching element Q1 with the first voltage
error signal based on the first output voltage Vo1. As is apparent
for a person skilled in the art, the same result will be obtained
by controlling an ON period of the second switching element Q2 with
the first voltage error signal based on the first output voltage
Vo1 and controlling an ON period of the first switching element Q1
with the second voltage error signal based on the second output
voltage Vo2.
[0073] According to this embodiment, a voltage obtained from one of
the first rectifying-smoothing circuit and second
rectifying-smoothing circuit is used to determine an ON period of
the first switching element and change duties of the first
switching element and second switching element, thereby controlling
the voltage of the first current resonant capacitor of the first
series resonant circuit. Also, a voltage obtained from the other of
the first rectifying-smoothing circuit and second
rectifying-smoothing circuit is used to determine an ON period of
the second switching element and change a switching frequency,
thereby controlling energy to be accumulated in the second resonant
capacitor of the second series resonant circuit. By controlling an
ON period of any one of the first switching element and second
switching element, it is possible to adjust output voltages and
stabilize the two outputs.
Embodiment 2
[0074] FIG. 6 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 2 of the present invention. This multiple output
switching power source apparatus differs from that of the
embodiment 1 in the configuration and operation of the secondary
side of a transformer T1. In the following, parts that differ from
those of the embodiment 1 will mainly be explained.
[0075] On the secondary side of the transformer T1, there are
arranged a first rectifying-smoothing circuit connected to a
secondary winding S1 (the number of turns of N2) that is wound to
generate a voltage whose phase is opposite to the phase of a
voltage of a primary winding P1 of the transformer T1, a second
series resonant circuit connected in parallel with the secondary
winding S1, and a second rectifying-smoothing circuit connected to
the second series resonant circuit.
[0076] The first rectifying-smoothing circuit has a diode D1, a
smoothing capacitor C1, and a diode D3. An anode of the diode D1 is
connected to a first end of the secondary winding S1 and a cathode
thereof is connected to a first output terminal. The smoothing
capacitor C1 is connected between the cathode of the diode D1 (the
first output terminal) and a ground terminal. An anode of the diode
D3 is connected to the ground terminal and a cathode thereof is
connected to a second end of the secondary winding S1. The first
rectifying-smoothing circuit rectifies and smoothes a voltage
induced by the secondary winding S1 of the transformer T1 and
outputs a first output voltage Vo1 from the first output
terminal.
[0077] The second series resonant circuit has a second resonant
reactor Lr2 whose first end is connected to the first end of the
secondary winding S1 (the anode of the diode D1) and a second
current resonant capacitor Cri2 connected between a second end of
the second resonant reactor Lr2 and the second end of the secondary
winding S1 (the cathode of the diode D3).
[0078] The second rectifying-smoothing circuit has a diode D2, a
smoothing capacitor C2, and a diode D4. An anode of the diode D2 is
connected to a connection point of the second resonant reactor Lr2
and second current resonant capacitor Cri2 and a cathode thereof is
connected to a second output terminal. The smoothing capacitor C2
is connected between the cathode of the diode D2 (the second output
terminal) and the ground terminal. An anode of the diode D4 is
connected to the ground terminal and a cathode thereof is connected
to the first end of the secondary winding S1 (the anode of the
diode D1). The second rectifying-smoothing circuit rectifies and
smoothes the sum of a voltage generated by the secondary winding S1
of the transformer T1 and a terminal voltage of the second current
resonant capacitor Cri2 and outputs a second output voltage Vo2
from the second output terminal.
[0079] Operation of the multiple output switching power source
apparatus according to the embodiment 2 of the present invention
configured as mentioned above will be explained with reference to
waveforms illustrated in FIG. 7. The meanings of marks illustrated
in FIG. 7 are the same as those of FIG. 5.
[0080] Control of the first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling the duties of a first switching element Q1 and
a second switching element Q2. Namely, by changing the ON-period
duty ratios of the first switching element Q1 and second switching
element Q2, a voltage stored in a first current resonant capacitor
Cri during an ON period of the first switching element Q1 is
adjusted, and in an ON period of the second switching element Q2,
energy accumulated in the first current resonant capacitor Cri
makes a first resonant reactor Lr and the first current resonant
capacitor Cri resonate. This results in passing a resonant current
through transmit energy to the secondary side. Namely, changing the
duty ratios can control the energy to be transmitted to the
secondary side. A voltage generated by the secondary winding S1 is
rectified and smoothed by the first rectifying-smoothing circuit
having the diode D1, diode D3, and smoothing capacitor C1, to
output the first output voltage Vo1 from the first output
terminal.
[0081] Control of the second output voltage Vo2 will be explained.
The second series resonant circuit having the second current
resonant capacitor Cri2 and second resonant reactor Lr2 has a
connection configuration that is opposite to that of the multiple
output switching power source apparatus according to the embodiment
1. Namely, in an ON period (for example, time t2 to t4) of the
second switching element Q2, a voltage of (Vo1+Vf) generated by the
secondary winding S1 is applied to produce a resonant operation
that accumulates energy in the second current resonant capacitor
Cri2.
[0082] In an ON period of the first switching element Q1, a voltage
obtained by adding a voltage corresponding to the energy
accumulated in the second current resonant capacitor Cri2 to a
voltage generated by the secondary winding S1 is rectified and
smoothed through the second rectifying-smoothing circuit having the
diode D2, smoothing capacitor C2, and diode D4, to output the
second output voltage Vo2 from the second output terminal. At this
time, the second current resonant capacitor Cri2 generates the
voltage corresponding to the energy accumulated therein, and
thereafter, is reversely charged by the voltage of the secondary
winding S1. When the charging of the smoothing capacitor C2 ends,
the diode D2 passes no current and the second current resonant
capacitor Cri2 gradually discharges due to a resonant operation
with the second resonant reactor Lr2 and is then reversely charged.
During this operation, the second switching element Q2 turns off
and the first switching element Q1 turns on, so that the secondary
winding S1 reversely induces a voltage and the discharging and
reverse charging operations continue.
[0083] In this way, the second current resonant capacitor Cri2
discharges only during a period in which the second switching
element Q2 turns on to charge the smoothing capacitor C2 and is
charged during the remaining ON period of the second switching
element Q2 and an ON period of the first switching element Q1.
Namely, except the period of charging the smoothing capacitor C2,
the second current resonant capacitor Cri2 is charged in most of a
switching period of the first switching element Q1 and second
switching element Q2. Namely, by changing the switching period,
i.e., switching frequency of the first switching element Q1 and
second switching element Q2, it is possible to adjust the charging
period of the second current resonant capacitor Cri2 and thereby
control the second output voltage Vo2. More precisely, according to
a second output voltage error signal provided by a feedback circuit
6, an ON period of the second switching element Q2 is controlled,
and according to a first output voltage error signal provided by a
feedback circuit 5, an ON period of the first switching element Q1
is controlled, to adjust duties of the first switching element Q1
and second switching element Q2. Namely, the first output voltage
error signal determines the duties and adjusts the first output
voltage, and therefore, controlling an ON period of the second
switching element according to the second output voltage error
signal results in changing the switching frequency and adjusting
the second output voltage.
[0084] The above-mentioned multiple output switching power source
apparatus according to the embodiment 2 controls an ON period of
the second switching element Q2 with the second voltage error
signal based on the second output voltage Vo2 and controls an ON
period of the first switching element Q1 with the first voltage
error signal based on the first output voltage Vo1. As is apparent
for a person skilled in the art, the same result will be obtained
by controlling an ON period of the second switching element Q2 with
the first voltage error signal based on the first output voltage
Vo1 and controlling an ON period of the first switching element Q1
with the second voltage error signal based on the second output
voltage Vo2.
[0085] If an input voltage Vin decreases, the first output voltage
Vo1 is kept constant by changing the duties of the first switching
element Q1 and second switching element Q2 so that the voltage of
the first current resonant capacitor Cri is kept constant. As a
result, in an ON period of the first switching element Q1, the
voltage generated by the secondary winding S1 decreases. To cope
with this, the above-mentioned multiple output switching power
source apparatus according to the embodiment 2 can decrease the
switching frequency if the voltage generated by the secondary
winding S1 decreases in an ON period of the first switching element
Q1, to thereby control energy to be accumulated in the second
current resonant capacitor Cri2, so that, even if an input voltage
decreases, constant power may be output to the second output
terminal.
[0086] This embodiment can adjust, like the embodiment 1, output
voltages by controlling any of the first switching element and
second switching element, to stabilize the two outputs.
Embodiment 3
[0087] FIG. 8 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 3 of the present invention. This multiple output
switching power source apparatus differs from that of the
embodiment 1 in the configuration of the secondary side of a
transformer. In the following, parts that differ from those of the
embodiment 1 will mainly be explained.
[0088] The transformer T2 has a first secondary winding S1 (the
number of turns of N2) that is wound to generate a voltage whose
phase is opposite to the phase of a voltage of a primary winding P1
and a second secondary winding S2 (the number of turns of N3) that
is wound to generate a voltage whose phase is opposite to the phase
of the voltage of the primary winding P1. The first secondary
winding S1 and second secondary winding S2 are wound into a tight
coupling. On the secondary side of the transformer T2, there are
arranged a first rectifying-smoothing circuit connected to the
first secondary winding S1 (the number of turns of N2), a second
series resonant circuit connected in parallel with the second
secondary winding S2, and a second rectifying-smoothing circuit
connected to the second series resonant circuit. The configuration
and operation of the first rectifying-smoothing circuit are the
same as those of the embodiment 1.
[0089] The second series resonant circuit has a second current
resonant capacitor Cri2 whose first end is connected to a first end
of the second secondary winding S2 and a second resonant reactor
Lr2 connected between a second end of the second current resonant
capacitor Cri2 and a second end of the second secondary winding S2
(a ground terminal).
[0090] The second rectifying-smoothing circuit has a diode D2 and a
smoothing capacitor C2. An anode of the diode D2 is connected to a
connection point of the second resonant reactor Lr2 and second
current resonant capacitor Cri2 and a cathode thereof is connected
to a second output terminal. The smoothing capacitor C2 is
connected between the cathode of the diode D2 (the second output
terminal) and the ground terminal. The second rectifying-smoothing
circuit rectifies and smoothes the sum of a voltage generated by
the second secondary winding S2 of the transformer T2 and a
terminal voltage of the second current resonant capacitor Cri2 and
outputs a second output voltage Vo2 from the second output
terminal.
[0091] Operation of the multiple output switching power source
apparatus according to the embodiment 3 of the present invention
configured as mentioned above will be explained with reference to
waveforms illustrated in FIG. 9. The meanings of marks illustrated
in FIG. 9 are the same as those of FIG. 5.
[0092] Control of the first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling the duties of a first switching element Q1 and
a second switching element Q2. Namely, by changing ON-period duty
ratios of the first switching element Q1 and second switching
element Q2, a voltage stored in a first current resonant capacitor
Cri during an ON period of the first switching element Q1 is
adjusted. As a result, in an ON period of the second switching
element Q2, energy accumulated in the first current resonant
capacitor Cri makes a first resonant reactor Lr and the first
current resonant capacitor Cri resonate and a resonant current
passes to transmit energy to the secondary side. Consequently,
changing the duty ratios can control the energy to be transmitted
to the secondary side. A voltage generated by the first secondary
winding S1 is rectified and smoothed by the first
rectifying-smoothing circuit having the diode D1 and smoothing
capacitor C1, to output the first output voltage Vo1 from the first
output terminal.
[0093] Control of the second output voltage Vo2 will be explained.
Like the multiple output switching power source apparatus according
to the embodiment 1, in an ON period (for example, time t1 to t2)
of the first switching element Q1, a differential voltage between
an input voltage Mm and a terminal voltage of the first current
resonant capacitor Cri is applied to the primary winding P1, and
therefore, the second secondary winding S2 generates a voltage that
is the differential voltage multiplied by a turn ratio. The voltage
generated by the second secondary winding S2 is applied to the
second series resonant circuit having the second current resonant
capacitor Cri2 and second resonant reactor Lr2, so that the second
series resonant circuit resonates to gradually charge the second
current resonant capacitor Cri2.
[0094] In an ON period of the second switching element Q2, a
voltage corresponding to energy accumulated in the second current
resonant capacitor Cri2 is added to a voltage generated by the
second secondary winding S2 and the resultant voltage is rectified
and smoothed through the second rectifying-smoothing circuit having
the diode D2 and smoothing capacitor C2, to output the second
output voltage Vo2 from the second output terminal. At this time,
the second current resonant capacitor Cri2 discharges the voltage
corresponding to the accumulated energy to once decrease the
voltage, and thereafter, is charged by a current in a reverse
direction due to the voltage of the secondary winding S2. When the
charging of the smoothing capacitor C2 ends, the diode D2 passes no
current and the second current resonant capacitor Cri2 gradually
discharges due to a resonant operation with the second resonant
reactor Lr2 and is then charged in a reverse manner. During this
operation, the second switching element Q2 turns off and the first
switching element Q1 turns on, so that the secondary winding S2
reversely induces a voltage and the discharging and reverse
charging operations continue.
[0095] In this way, the second current resonant capacitor Cri2
discharges only during a period in which the second switching
element Q2 turns on to charge the smoothing capacitor C2 and is
charged during the remaining ON period of the second switching
element Q2 and an ON period of the first switching element Q1.
Namely, except the period of charging the smoothing capacitor C2,
the second current resonant capacitor Cri2 is charged in most of a
switching period of the first switching element Q1 and second
switching element Q2. Namely, by changing the switching period,
i.e., switching frequency of the first switching element Q1 and
second switching element Q2, it is possible to adjust the charging
period of the second current resonant capacitor Cri2 and thereby
control the second output voltage Vo2. More precisely, according to
a second output voltage error signal provided by a feedback circuit
6, an ON period of the second switching element Q2 is controlled,
and according to a first output voltage error signal provided by a
feedback circuit 5, an ON period of the first switching element Q1
is controlled, to adjust duties of the first switching element Q1
and second switching element Q2. Namely, the first output voltage
error signal determines the duties and adjusts the first output
voltage, and therefore, controlling an ON period of the second
switching element according to the second output voltage error
signal results in changing the switching frequency and adjusting
the second output voltage.
[0096] The above-mentioned multiple output switching power source
apparatus according to the embodiment 3 controls an ON period of
the second switching element Q2 with the second voltage error
signal based on the second output voltage Vo2 and controls an ON
period of the first switching element Q1 with the first voltage
error signal based on the first output voltage Vo1. It is noted
that the same result will be obtained by controlling an ON period
of the second switching element Q2 with the first voltage error
signal based on the first output voltage Vo1 and controlling an ON
period of the first switching element Q1 with the second voltage
error signal based on the second output voltage Vo2.
[0097] If an input voltage Vin decreases, the first output voltage
Vo1 is kept constant by changing duties of the first switching
element Q1 and second switching element Q2 so that the voltage of
the first current resonant capacitor Cri is kept constant. As a
result, in an ON period of the first switching element Q1, the
voltage generated by the second secondary winding S2 decreases. To
cope with this, the above-mentioned multiple output switching power
source apparatus according to the embodiment 3 can decrease the
switching frequency if the voltage generated by the second
secondary winding S2 decreases in an ON period of the first
switching element Q1, to thereby control energy to be accumulated
in the second current resonant capacitor Cri2, so that, even if an
input voltage decreases, constant power may be output to the second
output terminal.
[0098] At this time, the first secondary winding S1 and second
secondary winding S2 are tightly coupled with each other, and
therefore, voltages generated by them are clamped at low voltages.
As illustrated in waveforms of FIG. 9, periods for sending energy
to the first output voltage Vo1 and second output voltage Vo2 are
completely separated into individual periods to narrow conduction
angles and increase current peaks. To solve this problem, the
multiple output switching power source apparatus according to the
embodiment 3 may be modified, as illustrated in FIG. 11 for
example, to shift the winding positions of the first secondary
winding S1 and second secondary winding S2 of the transformer T2
and loosely couple them with each other. This modification may make
current changes gentler and suppress current peaks, as illustrated
in waveforms of FIG. 10.
[0099] To suppress current peaks, there is a configuration of,
other than the technique of loosely coupling the first secondary
winding S1 and second secondary winding S2 with each other,
inserting a first reactor in a line from the second secondary
winding S2 to the second rectifying-smoothing circuit, i.e.,
between the second current resonant capacitor Cri2 and the anode of
the diode D2 (before or after a connection point with the second
resonant reactor). This configuration provides the same effect as
that mentioned above.
[0100] The first reactor may be formed by using a leakage
inductance to be generated when loosely coupling the first
secondary winding and second secondary winding of the transformer
T2 with each other. These techniques are applicable to the
above-mentioned multiple output switching power source apparatus
according to the embodiment 1, to provide the same effect as that
mentioned above. Namely, it is possible to widen periods in which
currents pass through the first rectifying-smoothing circuit and
second rectifying-smoothing circuit and suppress peak currents,
thereby reducing losses in the rectifying-smoothing circuits.
[0101] Only by adding a few parts to the conventional multiple
output switching power source apparatus, this embodiment can, like
the invention of the embodiment 1, adjust output voltages by
controlling any of ON periods of the first switching element and
second switching element and stabilize the two outputs.
Embodiment 4
[0102] FIG. 12 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 4 of the present invention and FIG. 13 is a waveform
diagram illustrating the operation thereof.
[0103] The meanings of marks in FIG. 13 are the same as those of
FIG. 5. FIG. 13 illustrates waveforms with a first secondary
winding S1 and second secondary winding S2 of a transformer T2
being loosely coupled with each other, or a first reactor being
inserted.
[0104] This multiple output switching power source apparatus
reverses the polarities of the second secondary winding S2 of the
multiple output switching power source apparatus according to the
embodiment 3. In the following, parts that differ from those of the
embodiment 1 will mainly be explained.
[0105] Control of a first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling the duties of a first switching element Q1 and
a second switching element Q2. Namely, by changing the duty ratios
of the first switching element Q1 and second switching element Q2,
a voltage stored in a first current resonant capacitor Cri during
an ON period of the first switching element Q is adjusted. In an ON
period of the second switching element Q2, energy accumulated in
the first current resonant capacitor Cri makes a first resonant
reactor Lr and the first current resonant capacitor Cri resonate.
As a result, a resonant current passes to transmit energy to the
secondary side of a transformer T2, thereby controlling the energy
to be transmitted to the secondary side. A voltage generated by a
first secondary winding S1 is rectified and smoothed by a first
rectifying-smoothing circuit having a diode D1 and smoothing
capacitor C1, to output the first output voltage Vo1 from a first
output terminal.
[0106] Control of a second output voltage Vo2 will be explained. A
second series resonant circuit having a second current resonant
capacitor Cri2 and second resonant reactor Lr2 conducts, in an ON
period of the second switching element Q2, a resonant operation
with a voltage of (Vo1+Vf) generated by the first secondary winding
S1, to accumulate energy in the second current resonant capacitor
Cri2. In an ON period of the first switching element Q1, a voltage
obtained by adding a voltage corresponding to the energy
accumulated in the second current resonant capacitor Cri2 to a
voltage generated by the first secondary winding S1 is rectified
and smoothed through a second rectifying-smoothing circuit having a
diode D2 and smoothing capacitor C2, to output the second output
voltage Vo2 from a second output terminal. At this time, the second
current resonant capacitor Cri2 decreases the voltage corresponding
to the energy accumulated therein due to discharge, and thereafter,
is charged by a current in a reverse direction due to the voltage
of the secondary winding S1. When the charging of the smoothing
capacitor C2 ends, the diode D2 passes no current and the second
current resonant capacitor Cri2 gradually discharges due to a
resonant operation with the second resonant reactor Lr2 and is then
charged reversely. During this operation, the second switching
element Q2 turns off and the first switching element Q1 turns on,
so that the secondary winding S1 reversely induces a voltage and
the discharging and reverse charging operations continue.
[0107] In this way, the second current resonant capacitor Cri2
discharges only during a period in which the second switching
element Q2 turns on to charge the smoothing capacitor C2 and is
charged during the remaining ON period of the second switching
element Q2 and an ON period of the first switching element Q1.
Namely, except the period of charging the smoothing capacitor C2,
the second current resonant capacitor Cri2 is charged in most of a
switching period of the first switching element Q1 and second
switching element Q2. By changing the switching period, i.e.,
switching frequency of the first switching element Q1 and second
switching element Q2, it is possible to adjust the charging period
of the second current resonant capacitor Cri2 and thereby control
the second output voltage Vo2. More precisely, according to a
second output voltage error signal provided by a feedback circuit
6, an ON period of the second switching element Q2 is controlled,
and according to a first output voltage error signal provided by a
feedback circuit 5, an ON period of the first switching element Q1
is controlled, to adjust duties of the first switching element Q1
and second switching element Q2. The first output voltage error
signal determines the duties and adjusts the first output voltage,
and therefore, controlling an ON period of the second switching
element according to the second output voltage error signal results
in changing the switching frequency and adjusting the second output
voltage.
[0108] The above-mentioned multiple output switching power source
apparatus according to the embodiment 4 controls an ON period of
the second switching element Q2 with the second voltage error
signal based on the second output voltage Vo2 and controls an ON
period of the first switching element Q1 with the first voltage
error signal based on the first output voltage Vo1. It is noted
that the same result will be obtained by controlling an ON period
of the second switching element Q2 with the first voltage error
signal based on the first output voltage Vo1 and controlling an ON
period of the first switching element Q1 with the second voltage
error signal based on the second output voltage Vo2.
[0109] Like the embodiment 2, this embodiment can output constant
power to the second output terminal even if an input voltage
decreases.
[0110] This embodiment loosely couples the first secondary winding
and second secondary winding of the transformer with each other, to
increase a leakage inductance, suppress current peaks, and reduce
losses in the rectifying-smoothing circuits.
Embodiment 5
[0111] FIG. 14 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 5 of the present invention and FIG. 15 is a waveform
diagram illustrating the operation thereof. The meanings of marks
in FIG. 15 are the same as those of FIG. 5.
[0112] The multiple output switching power source apparatus
according to the embodiment 5 is configured such that the second
resonant reactor Lr2 of the multiple output switching power source
apparatus according to the embodiment 1 illustrated in FIG. 4 is
included in a primary winding P2 (the number of turns of N4) of a
second transformer T3 and a voltage generated by a secondary
winding S3 (the number of turns of N5) of the second transformer T3
is rectified and smoothed through a second rectifying-smoothing
circuit having a diode D2 and smoothing capacitor C2, to output a
second output voltage Vo2 from a second output terminal. In the
following, parts that differ from those of the embodiment 1 will
mainly be explained.
[0113] Control of a first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling the ON-period duties of a first switching
element Q1 and a second switching element Q2. Namely, by changing
the duty ratios of the first switching element Q1 and second
switching element Q2, a voltage stored in a first current resonant
capacitor Cri during an ON period of the first switching element Q1
is adjusted. In an ON period of the second switching element Q2,
energy accumulated in the first current resonant capacitor Cri
makes a first resonant reactor Lr and the first current resonant
capacitor Cri resonate, so that a resonant current passes to
transmit energy to the secondary side. Namely, by controlling the
ON periods of Q1 and Q2, it is possible to control the energy to be
transmitted to the secondary side. A voltage generated by a first
secondary winding S1 is rectified and smoothed by a first
rectifying-smoothing circuit having a diode D1 and smoothing
capacitor C1, to output the first output voltage Vo1 from a first
output terminal.
[0114] Control of the second output voltage Vo2 will be explained.
Like the multiple output switching power source apparatus according
to the embodiment 1, in an ON period of the first switching element
Q1, a differential voltage between an input voltage Vin and a
terminal voltage of the first current resonant capacitor Cri is
applied to the primary winding P1, and therefore, the second
secondary winding S3 generates a voltage that is the differential
voltage multiplied by a turn ratio. The voltage generated by the
second secondary winding S3 is applied to a second series resonant
circuit having a second current resonant capacitor Cri2 and the
second resonant reactor Lr2, so that the second series resonant
circuit resonates to gradually charge the second current resonant
capacitor Cri2.
[0115] In an ON period of the second switching element Q2, the
secondary winding S3 of the second transformer T3 generates a
voltage that is obtained by multiplying the sum of a voltage
generated by the first secondary winding S1 and a voltage
corresponding to energy accumulated in the second current resonant
capacitor Cri2 by a turn ratio. The generated voltage is rectified
and smoothed through the second rectifying-smoothing circuit having
the diode D2 and smoothing capacitor C2, to output the second
output voltage Vo2 from the second output terminal. At this time,
the second current resonant capacitor Cri2 discharges to decrease
the voltage corresponding to the accumulated energy, and
thereafter, is charged by a current flowing in a reverse direction
due to the voltage of the secondary winding S1. When the charging
of the smoothing capacitor C2 ends, the diode D2 passes no current
and the second current resonant capacitor Cri2 gradually discharges
due to a resonant operation with the second resonant reactor Lr2
and is then charged in a reverse manner. During this operation, the
second switching element Q2 turns off and the first switching
element Q1 turns on, so that the secondary winding S1 reversely
induces a voltage and the discharging and reverse charging
operations continue.
[0116] In this way, the second current resonant capacitor Cri2
discharges only during a period in which the second switching
element Q2 turns on to charge the smoothing capacitor C2 and is
charged during the remaining ON period of the second switching
element Q2 and an ON period of the first switching element Q1.
Namely, except the period of charging the smoothing capacitor C2,
the second current resonant capacitor Cri2 is charged in most of a
switching period of the first switching element Q1 and second
switching element Q2. By changing the switching period, i.e.,
switching frequency of the first switching element Q1 and second
switching element Q2, it is possible to adjust the charging period
of the second current resonant capacitor Cri2 and thereby control
the second output voltage Vo2. More precisely, according to a
second output voltage error signal provided by a feedback circuit
6, an ON period of the second switching element Q2 is controlled,
and according to a first output voltage error signal provided by a
feedback circuit 5, an ON period of the first switching element Q1
is controlled, to adjust the duties of the first switching element
Q1 and second switching element Q2. Namely, the first output
voltage error signal determines the duties and adjusts the first
output voltage, and therefore, controlling an ON period of the
second switching element according to the second output voltage
error signal results in changing the switching frequency and
adjusting the second output voltage.
[0117] The above-mentioned multiple output switching power source
apparatus according to the embodiment 5 controls an ON period of
the second switching element Q2 with the second voltage error
signal based on the second output voltage Vo2 and controls an ON
period of the first switching element Q1 with the first voltage
error signal based on the first output voltage Vo1. The same result
will be obtained by controlling an ON period of the second
switching element Q2 with the first voltage error signal based on
the first output voltage Vo1 and controlling an ON period of the
first switching element Q1 with the second voltage error signal
based on the second output voltage Vo2.
[0118] The primary winding P2 and secondary winding S3 of the
second transformer T3 may loosely be coupled with each other to
increase a reactor component Like the multiple output switching
power source apparatus according to the modification of the
embodiment 3 and as illustrated in the waveforms of FIG. 10, it is
possible to suppress a current peak when outputting a voltage to
the first output terminal or the second output terminal, provide a
current that gently changes, and reduce losses in the
rectifying-smoothing circuits.
[0119] According to this embodiment, the second resonant reactor is
provided by the separate winding that forms the second transformer.
Since a voltage is adjustable according to a turn ratio of the
second transformer, an output voltage can freely be set without
regard to a turn ratio of the first transformer.
Embodiment 6
[0120] FIG. 16 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 6 of the present invention and FIG. 17 is a waveform
diagram illustrating the operation of the multiple output switching
power source apparatus. The meanings of marks in FIG. 17 are the
same as those of FIG. 5.
[0121] This multiple output switching power source apparatus
reverses the polarities of the secondary winding S3 of the second
transformer T3 in the multiple output switching power source
apparatus according to the embodiment 5. In the following, parts
that differ from those of the embodiment 1 will mainly be
explained.
[0122] Control of a first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling the duties of a first switching element Q1 and
a second switching element Q2. Namely, by changing the duty ratios
of the first switching element Q1 and second switching element Q2,
a voltage stored in a first current resonant capacitor Cri during
an ON period of the first switching element Q1 is adjusted. In an
ON period of the second switching element Q2, energy accumulated in
the first current resonant capacitor Cri makes a first resonant
reactor Lr and the first current resonant capacitor Cri produce a
resonant current that causes energy to be transmitted to the
secondary side, thereby controlling the energy to be transmitted to
the secondary side. A voltage generated by the first secondary
winding S1 is rectified and smoothed by a first
rectifying-smoothing circuit having a diode D1 and smoothing
capacitor C1, to output the first output voltage Vo1 from a first
output terminal.
[0123] Control of a second output voltage Vo2 will be explained. A
second series resonant circuit having a second current resonant
capacitor Cri2 and a primary winding P2 of the second transformer
T3 conducts, in an ON period of the second switching element Q2
contrary to the multiple output switching power source apparatus
according to the embodiment 1, a resonant operation by the
application of a voltage (Vo1+Vf) generated by the first secondary
winding S1, to accumulate energy in the second current resonant
capacitor Cri2.
[0124] In an ON period of the first switching element Q1, the
secondary winding S3 of the second transformer T3 generates a
voltage that is obtained by multiplying the sun of a voltage
generated by the first secondary winding S1 and a voltage
corresponding to the energy accumulated in the second current
resonant capacitor Cri2 by a turn ratio. The voltage is rectified
and smoothed through a second rectifying-smoothing circuit having a
diode D2 and smoothing capacitor C2, to output the second output
voltage Vo2 from a second output terminal. At this time, the second
current resonant capacitor Cri2 discharges to decrease the voltage
corresponding to the accumulated energy, and thereafter, is charged
by a current flowing in a reverse direction due to the voltage of
the secondary winding S3. When the charging of the smoothing
capacitor C2 ends, the diode D2 passes no current and the second
current resonant capacitor Cri2 gradually discharges due to a
resonant operation with a second resonant reactor Lr2 and is then
charged in a reverse manner. During this operation, the second
switching element Q2 turns off and the first switching element Q1
turns on, so that the secondary winding S3 reversely induces a
voltage and the discharging and reverse charging operations
continue.
[0125] In this case, a charging period of the second current
resonant capacitor Cri2 is determined by an ON period of the first
switching element Q1 and an ON period of the second switching
element Q2. At this time, the ON period of the first switching
element Q1 is controlled to the duty that may keep the first output
voltage Vo1 constant. Accordingly, controlling the ON period of the
second switching element Q2, i.e., changing the switching frequency
of the second switching element Q2 results in changing energy
accumulated in the second current resonant capacitor Cri2 and
controlling the second output voltage Vo2. Namely, a control
circuit 10a changes the ON period, i.e., switching frequency of the
second switching element Q2 in response to a second voltage error
signal sent from a feedback circuit 6, to control the second output
voltage Vo2 output from the second output terminal.
[0126] The above-mentioned multiple output switching power source
apparatus according to the embodiment 6 is configured to control an
ON period of the second switching element Q2 with the second
voltage error signal based on the second output voltage Vo2 and
control an ON period of the first switching element Q1 with the
first voltage error signal based on the first output voltage Vo1.
The same result will be obtained by controlling an ON period of the
second switching element Q2 with the first voltage error signal
based on the first output voltage Vo1 and controlling an ON period
of the first switching element Q1 with the second voltage error
signal based on the second output voltage Vo2.
[0127] Like the embodiment 2, it is possible to output constant
power to the second output terminal even if an input voltage
decreases.
[0128] According to the embodiments 1, 3, and 5, in an ON period of
the switching element Q2, a voltage generated by the secondary
winding is rectified and smoothed to provide the first output
voltage and a voltage of the second resonant reactor is rectified
and smoothed to provide the second output voltage. Instead, in an
ON period of the switching element Q1, a voltage generated by the
secondary winding may be rectified and smoothed to provide the
first output voltage and a voltage of the second resonant reactor
may be rectified and smoothed to provide the second output voltage,
to realize the same effect According to the embodiments 2, 4, and
6, in an ON period of the switching element Q2, a voltage generated
by the secondary winding is rectified and smoothed to provide the
first output voltage, and in an ON period of the switching element
Q1, a voltage of the second resonant reactor is rectified and
smoothed to provide the second output voltage. Instead, in an ON
period of the switching element Q1, a voltage generated by the
secondary winding may be rectified and smoothed to provide the
first output voltage, and in an ON period of the switching element
Q2, a voltage of the second resonant reactor may be rectified and
smoothed to provide the second output voltage, to realize the same
effect.
Embodiment 7
[0129] FIG. 18 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 7 of the present invention. In connection with this
multiple output switching power source apparatus, parts that differ
from those of the multiple output switching power source apparatus
according to the embodiment 6 will mainly be explained.
[0130] On the secondary side of a transformer T1, a secondary
winding S1 (the number of turns of N2) is wound to generate a
voltage whose phase is opposite to that of a voltage of a primary
winding P1 of the transformer T1. The secondary winding S1 (the
number of turns of N2) is connected in parallel with a first
rectifying-smoothing circuit and second series resonant circuit. A
second transformer T4 has a primary winding P2 (the number of turns
of N4) forming the second series resonant circuit, a first
secondary winding S3 (the number of turns of N5), and a second
secondary winding S4 (the number of turns of N6) connected in
series with the first secondary winding S3.
[0131] The first rectifying-smoothing circuit has a diode D1 and a
smoothing capacitor C1. An anode of the diode D1 is connected to a
first end of the secondary winding S1 and a cathode thereof is
connected to a first output terminal. The smoothing capacitor C1 is
connected between the cathode of the diode D1 (the first output
terminal) and a second end of the secondary winding S1 (a ground
terminal). The first rectifying-smoothing circuit rectifies and
smoothes a voltage induced by the secondary winding S1 of the
transformer T1 and outputs a first output voltage Vo1 from the
first output terminal.
[0132] The second series resonant circuit has a second current
resonant capacitor Cri2 whose first end is connected to the first
end of the secondary winding S1 of the transformer T1 (the anode of
the diode D1) and the primary winding P2 of the second transformer
T4 connected between a second end of the second current resonant
capacitor Cri2 and the second end of the secondary winding S1 (the
ground terminal). Namely, this is equivalent to the second series
resonant circuit of the embodiment 1 with the second resonant
reactor Lr2 being included in the primary winding P2 of the second
transformer T4.
[0133] A second rectifying-smoothing circuit has diodes D2 and D4
and a smoothing capacitor C2. An anode of the diode D2 is connected
to the first secondary winding S3 of the second transformer T4 and
a cathode thereof is connected to a second output terminal. An
anode of the diode D4 is connected to the second secondary winding
S4 of the second transformer T4 and a cathode thereof is connected
to the second output terminal. A connection point of the first
secondary winding S3 and second secondary winding S4 of the second
transformer T4 is connected to the ground terminal.
[0134] The smoothing capacitor C2 is connected between the cathodes
of the diodes D2 and D4 (the second output terminal) and the second
end of the secondary winding S1 (the ground terminal). The second
rectifying-smoothing circuit rectifies and smoothes a voltage that
is the sum of a voltage generated by the secondary winding S1 of
the transformer T1 and a terminal voltage of the second current
resonant capacitor Cri2 and outputs a second output voltage Vo2
from the second output terminal.
[0135] Further, this multiple output switching power source
apparatus has a feedback circuit 5 and a feedback circuit 6, to
feed voltages generated on the secondary side of the transformer T1
back to the primary side. The feedback circuit 5 compares the first
output voltage Vo1 output to the first output terminal with a
predetermined reference voltage and feeds an error voltage as a
first voltage error signal back to a control circuit 10a on the
primary side. The feedback circuit 6 compares the second output
voltage Vo2 output to the second output terminal with a
predetermined reference voltage and feeds an error voltage as a
second voltage error signal back to the control circuit 10a on the
primary side.
[0136] Based on the first voltage error signal from the feedback
circuit 5 and the second voltage error signal from the feedback
circuit 6, the control circuit 10a alternately turns on/off a first
switching element Q1 and a second switching element Q2, to carry
out PWM control so that the first output voltage Vo1 and second
output voltage Vo2 remain constant. In this case, gates of the
first switching element Q1 and second switching element Q2 receive
voltages as control signals that create a dead time of about
several hundreds of nanoseconds. As a result, the first switching
element Q1 and second switching element Q2 alternately turn on/off
without overlapping their ON periods with each other.
[0137] Operation of the multiple output switching power source
apparatus according to the embodiment 7 of the present invention
having the above-mentioned configuration will be explained with
reference to waveforms illustrated in FIG. 19. FIG. 19 is a
waveform diagram illustrating operation under heavy load. The
meanings of marks in FIG. 19 are the same as those of FIG. 5.
[0138] Control of the first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling duties of the first switching element Q1 and
second switching element Q2. Namely, by changing the duty ratios of
the first switching element Q1 and second switching element Q2, a
voltage stored in a first current resonant capacitor Cri during an
ON period of the first switching element Q1 is adjusted.
[0139] In an ON period of the second switching element Q2, energy
accumulated in the first current resonant capacitor Cri makes a
first resonant reactor Lr and the first current resonant capacitor
Cri resonate. As a result, a resonant current passes to transmit
energy to the secondary side of the transformer T1, and therefore,
it is possible to control the energy to be transmitted to the
secondary side. A voltage generated by the secondary winding S1 is
rectified and smoothed by the first rectifying-smoothing circuit
having the diode D1 and smoothing capacitor C1, to output the first
output voltage Vo1 from the first output terminal.
[0140] Control of the second output voltage Vo2 will be explained.
In an ON period (for example, time t1 to t2) of the first switching
element Q1, a differential voltage between an input voltage Vin and
a terminal voltage of the first current resonant capacitor Cri is
applied to the primary winding P1, and therefore, the secondary
winding S1 generates a voltage that is the differential voltage
multiplied by a turn ratio. The sum of this voltage and the voltage
of the second current resonant capacitor Cri2 is applied to the
primary winding P2 of the second transformer T4. Then, the second
secondary winding S4 of the second transformer T4 generates the
voltage multiplies by a turn ratio, to pass a current through a
path along S4, D4, C2, and S4. The voltage is rectified and
smoothed by the diode D4 and smoothing capacitor C2, to output the
second output voltage Vo2.
[0141] At the same time, the voltage generated by the secondary
winding S1 is applied to the second series resonant circuit having
the second current resonant capacitor Cri2 and second resonant
reactor Lr2, so that the second series resonant circuit resonates
to gradually discharge the second current resonant capacitor Cri2
and charge the same in a reverse manner.
[0142] In an ON period (for example, time t2 to t4) of the second
switching element Q2, a voltage generated by the secondary winding
S1 becomes higher than the output voltage Vo1 by a forward voltage
drop of the diode D1. The sum of this voltage and a voltage of the
second current resonant capacitor Cri2 is applied to the primary
winding P2 of the second transformer T4. As a result, the first
secondary winding S3 of the second transformer T4 generates the
voltage times a turn ratio, to pass a current through a path along
S3, D2, C2, and S3, so that the voltage is rectified and smoothed
by the diode D2 and smoothing capacitor C2, to output the second
output voltage Vo2.
[0143] At the same time, the voltage generated by the secondary
winding S1 is applied to the second series resonant circuit having
the second current resonant capacitor Cri2 and second resonant
reactor Lr2, to make the second series resonant circuit resonate.
As a result, the second current resonant capacitor Cri2 gradually
discharges and is charged reversely.
[0144] In this way, the second resonant capacitor Cri2 discharges
energy for the second output voltage Vo2 in ON periods of the first
switching element Q1 and second switching element Q2, and also, is
charged and discharged due to a series resonant operation caused by
a voltage generated by the first secondary winding S1. In this
resonant operation, the amplitude of the second current resonant
capacitor Cri2 is adjustable by changing a switching frequency.
Namely, lowering the switching frequency enlarges the amplitude of
the second current resonant capacitor Cri2 and increasing the
switching frequency makes the amplitude of the second current
resonant capacitor Cri2 smaller.
[0145] In addition, changing the amplitude of the second resonant
capacitor Cri2 changes energy to be sent for the second output Vo2.
Namely, changing a switching frequency results in adjusting the
charging period of the second current resonant capacitor Cri2 and
controlling the second output voltage Vo2. More precisely, the
second output voltage error signal provided by the feedback circuit
6 is used to control an ON period of the second switching element
Q2 and the first output voltage error signal provided by the
feedback circuit 5 is used to control an ON period of the first
switching element Q1, to thereby adjust duties of the first
switching element Q1 and second switching element Q2. Namely, the
first output voltage error signal determines the duties to adjust
the first output voltage Vo1, and therefore, controlling an ON
period of the second switching element Q2 according to the second
output voltage error signal results in changing the switching
frequency and adjusting the second output voltage Vo2.
[0146] The above-mentioned multiple output switching power source
apparatus according to the embodiment 7 controls an ON period of
the second switching element Q2 with the second voltage error
signal based on the second output voltage Vo2 and controls an ON
period of the first switching element Q1 with the first voltage
error signal based on the first output voltage Vo1. It is noted
that the same result will be obtained by controlling an ON period
of the second switching element Q2 with the first voltage error
signal based on the first output voltage Vo1 and controlling an ON
period of the first switching element Q1 with the second voltage
error signal based on the second output voltage Vo2.
[0147] This embodiment can provide the same effect as that provided
by the invention of the embodiment 1 and can further stabilize the
second output voltage because the second rectifying-smoothing
circuit rectifies and smoothes voltages generated by a plurality of
secondary windings of the second transformer.
[0148] According to the invention of this embodiment, a current
passes through the first diode to the smoothing capacitor when the
first switching element is ON (or OFF) and a current passes through
the second diode to the smoothing capacitor when the first
switching element is OFF (or ON), to reduce a ripple component and
further stabilize the second output voltage.
Embodiment 8
[0149] FIG. 20 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 8 of the present invention. This multiple output
switching power source apparatus is characterized in that, compared
with the multiple output switching power source apparatus of the
embodiment 7 illustrated in FIG. 18, a secondary winding of a
transformer T2 includes a first secondary winding S1 and a second
secondary winding S2 (the number of turns of N3), a first
rectifying-smoothing circuit rectifies and smoothes a voltage
generated by the first secondary winding S1 of the transformer T2,
and a second series resonant circuit is connected in parallel with
the second secondary winding S2 of the transformer T2. The
remaining configuration thereof is similar to the configuration of
the embodiment 7.
[0150] According to the embodiment 8 with such a configuration, the
second series resonant circuit conducts a resonant operation due to
a voltage generated by the second secondary winding S2 of the
transformer T2 and operates like the embodiment 7, to realize a
similar effect Namely, only by adding the second secondary winding
S2 of the transformer T2 to the configuration of the embodiment 7,
controlling the ON period of any one of first switching element Q1
and second switching element Q2 results in adjusting output
voltages like the above-mentioned invention of the embodiment 7, to
stabilize the two outputs.
[0151] In addition, when the first switching element Q1 is ON, a
current passes through a diode D4 to a capacitor C2, and when the
first switching element Q1 is OFF, a current passes through a diode
D2 to the capacitor C2, to thereby reduce a ripple component and
further stabilize the second output voltage Vo2.
[0152] The second secondary winding S2 of the transformer T2
illustrated in FIG. 20 has polarities with a lower side being a
winding start (black dot mark). For example, it may have polarities
with an upper side being a winding start.
[0153] This embodiment only adds the second secondary winding of
the first transformer to the invention of the embodiment 7, to
control the ON period of any one of the first switching element and
second switching element and adjust and stabilize the two output
voltages.
Embodiment 9
[0154] FIG. 21 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 9 of the present invention. According to the
embodiments 1 to 8, the second series resonant circuit for
generating the second output voltage is arranged on the secondary
side of a transformer. Arranging the same on the primary side of
the transformer can also constitute a multiple output switching
power source apparatus.
[0155] More precisely, this multiple output switching power source
apparatus has, on the primary side of a first transformer T1A, a
full-wave rectifying circuit 2 to rectify an AC voltage from a
commercial power source 1, a smoothing capacitor C3 connected
between output terminals of the full-wave rectifying circuit 2, to
smooth an output from the full-wave rectifying circuit 2, a first
switching element Q1 and a second switching element Q2 that are
connected in series between both ends of the smoothing capacitor
C3, to receive a terminal voltage of the smoothing capacitor C3 as
a DC input voltage Vin, a control circuit 10a to control ON/OFF of
the first switching element Q1 and second switching element Q2, a
voltage resonant capacitor Crv connected in parallel with the
second switching element Q2, and a first series resonant circuit
connected to both ends of the voltage resonant capacitor Crv.
[0156] The first series resonant circuit has a primary winding P1
(the number of turns of N1) of the first transformer T1A, a first
resonant reactor Lr, and a first current resonant capacitor Cri
that are connected in series. The first resonant reactor Lr is, for
example, a leakage inductance between the primary and secondary
sides of the first transformer T1A.
[0157] On the secondary side of the transformer T1A, a first
rectifying-smoothing circuit is connected to a secondary winding S1
(the number of turns of N2) that is wound to generate a voltage
whose phase is opposite to the phase of a voltage of the primary
winding P1 of the transformer T1A.
[0158] The first rectifying-smoothing circuit has a diode D1 and a
smoothing capacitor C1. An anode of the diode D1 is connected to a
first end of the secondary winding S1 and a cathode thereof is
connected to a first output terminal. The smoothing capacitor C1 is
connected between the cathode of the diode D1 (the first output
terminal) and a second end of the secondary winding S1 (a ground
terminal). The first rectifying-smoothing circuit rectifies and
smoothes a voltage induced by the secondary winding S1 of the
transformer T1A and outputs a first output voltage Vo1 from the
first output terminal.
[0159] Both ends of the primary winding of the transformer T1A are
provided with a second series resonant circuit. The second series
resonant circuit has a second resonant reactor Lr2 having a first
end connected to a connection point of the switching element Q1 and
switching element Q2 and a second end connected to a first end of a
primary winding P2 of a second transformer T1B and a second current
capacitor Cri2 having a first end connected to a second end of the
primary winding P2 and a second end connected to a connection point
of a second end of the transformer T1A and the first resonant
capacitor Cri. The second resonant reactor Lr2 is, for example, a
leakage inductance between the primary and secondary sides of the
second transformer T1B. On the secondary side of the second
transformer T1B, a second rectifying-smoothing circuit is connected
to a secondary winding S2 (the number of turns of N4) that is wound
to generate a voltage whose phase is the same as the phase of a
voltage of the primary winding P2 of the second transformer
T1B.
[0160] The second rectifying-smoothing circuit has a diode D2 and a
smoothing capacitor C2. An anode of the diode D2 is connected to
the secondary winding S2 of the second transformer T1B and a
cathode thereof is connected to a second output terminal. The
smoothing capacitor C2 is connected between the cathode of the
diode D2 (the second output terminal) and the second end of the
secondary winding S2 (the ground terminal).
[0161] This multiple output switching power source apparatus has a
feedback circuit 5 and a feedback circuit 6, to feed the first
output voltage Vo1 and second output voltage Vo2 back to the
primary side. The feedback circuit 5 compares the first output
voltage Vo1 output to the first output terminal with a
predetermined reference voltage and feeds an error voltage as a
first voltage error signal back to the control circuit 10a on the
primary side. The feedback circuit 6 compares the second output
voltage Vo2 output to the second output terminal with a
predetermined reference voltage and feeds an error voltage as a
second voltage error signal back to the control circuit 10a on the
primary side.
[0162] Based on the first voltage error signal from the feedback
circuit 5 and the second voltage error signal from the feedback
circuit 6, the control circuit 10a alternately turns on/off the
first switching element Q1 and second switching element Q2, to
carry out PWM control so that the first output voltage Vo1 and
second output voltage Vo2 remain constant. In this case, gates of
the first switching element Q1 and second switching element Q2
receive voltages as control signals that create a dead time of
about several hundreds of nanoseconds. As a result, the first
switching element Q1 and second switching element Q2 alternately
turn on/off without overlapping their ON periods with each
other.
[0163] Operation of the multiple output switching power source
apparatus according to the embodiment 9 of the present invention
having the above-mentioned configuration will be explained with
reference to waveforms illustrated in FIGS. 22 and 23.
[0164] In FIGS. 22 and 23, VQ2ds is a drain-source voltage of the
second switching element Q2, IQ1 a current passing through a drain
of the first switching element Q1, IQ2 a current passing through a
drain of the second switching element Q2, Icri a current passing
through first current resonant capacitor Cri, Vcri a terminal
voltage of the first current resonant capacitor Cri, Icri2 a
current passing through the second current resonant capacitor Cri2,
Vcir2 a terminal voltage of the second current resonant capacitor
Cri2, ID1 a current passing through the diode D1, and ID2 a current
passing through the diode D2.
[0165] Control of the first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling duties of the first switching element Q1 and
second switching element Q2. Namely, by changing the ON-period duty
ratios of the first switching element Q1 and second switching
element Q2, a voltage stored in the first current resonant
capacitor Cri during an ON period of the first switching element Q1
is adjusted, and in an ON period of the second switching element
Q2, energy accumulated in the first current resonant capacitor Cri
makes the first resonant reactor Lr and first current resonant
capacitor Cri resonate. As a result, a resonant current passes to
transmit energy to the secondary side of the first transformer T1A,
and therefore, it is possible to control the energy to be
transmitted to the secondary side. A voltage generated by the
secondary winding S1 is rectified and smoothed by the first
rectifying-smoothing circuit consisting of the diode D1 and
smoothing capacitor C1, to output the first output voltage Vo1 from
the first output terminal.
[0166] Control of the second output voltage Vo2 will be explained.
In an ON period (for example, time t2 to t4) of the second
switching element Q2, a differential voltage between the sum of an
input voltage and a voltage of the second resonant capacitor Cri2
and a voltage of the first current resonant capacitor Cri is
applied to the primary winding P2 of the second transformer T1B and
the second resonant reactor Lri2, second resonant capacitor Cri2,
and first resonant capacitor Cri produce a resonant current to be
transmitted to the secondary side of the second transformer T1B.
The transmitted current is rectified and smoothed through the
second rectifying-smoothing circuit having the diode D2 and
smoothing capacitor C2, to output the second output voltage Vo2
from the second output terminal. At this time, the second current
resonant capacitor Cri2 discharges the voltage corresponding to the
accumulated energy, and thereafter, is reversely charged by a
differential voltage between the input voltage and the voltage of
the first resonant capacitor Cri. During this operation, the second
switching element Q2 turns off and the first switching element Q1
turns on, so that the voltage stored in the first resonant
capacitor Cri is applied to the second series resonant circuit. Due
to the resonant operation of the second series resonant circuit,
the first resonant capacitor Cri continues an reverse charging
operation. Thereafter, the resonant current of the second series
resonant circuit inverts to resume the above-mentioned forward
charging operation to accumulate energy in the second resonant
capacitor Cri2.
[0167] In this case, a charging period of the second current
resonant capacitor Cri2 is determined by an ON period of the first
switching element Q1 and an ON period of the second switching
element Q2. The ON period of the first switching element Q1 is
controlled to achieve duties that may keep the first output voltage
Vo1 constant. Accordingly, by controlling the ON period of the
second switching element Q2, a switching frequency of the second
switching element Q2 can be changed to change energy to be
accumulated in the second current resonant capacitor Cri2 and
thereby control the second output voltage Vo2. Namely, according to
the second voltage error signal sent from the feedback circuit 6,
the control circuit 10a changes the ON period, i.e., switching
frequency of the second switching element Q2, thereby controlling
the second output voltage Vo2 output from the second output
terminal.
[0168] As illustrated in FIG. 22, the waveforms under heavy load
indicate that the ON period of the switching element Q2 is long,
the amplitude of the second resonant capacitor Cri2 is large, and
energy transmitted to the secondary side is large. As illustrated
in FIG. 23, the waveforms under light load indicate that the ON
period of the switching element Q2 is short, the amplitude of the
second resonant capacitor Cri2 is small, and energy transmitted to
the secondary side is restricted. At this time, the ON period of
the switching element Q1 changes to maintain the first output
voltage Vo1 at a constant value according to changes in the ON
period of the switching element Q2, and therefore, is controlled
substantially at a constant duty.
[0169] The multiple output switching power source apparatus
according to this embodiment controls an ON period of the second
switching element Q2 with the second voltage error signal based on
the second output voltage Vo2 and controls an ON period of the
first switching element Q1 with the first voltage error signal
based on the first output voltage Vo1. It is noted that the same
result will be obtained by controlling an ON period of the second
switching element Q2 with the first voltage error signal based on
the first output voltage Vo1 and controlling an ON period of the
first switching element Q1 with the second voltage error signal
based on the second output voltage Vo2.
Embodiment 10
[0170] FIG. 24 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 10 of the present invention. The multiple output
switching power source apparatus of FIG. 24 differs from the
multiple output switching power source apparatus of the embodiment
9 of FIG. 21 in that a secondary winding of a second transformer
T1B is wound to generate a voltage whose phase is opposite to the
phase of a voltage of a primary winding P2. The remaining part
thereof is similar to the embodiment 9.
[0171] Operation of the multiple output switching power source
apparatus according to the embodiment 10 of the present invention
having such a configuration will be explained with reference to
waveforms illustrated in FIGS. 25 and 26. FIG. 25 illustrates
operational waveforms under heavy load on first and second outputs
and FIG. 26 illustrates operational waveforms under light load on
the second output
[0172] Control of a first output voltage Vo1 is carried out, like
the multiple output switching power source apparatus of the related
art, by controlling the duties of a first switching element Q1 and
a second switching element Q2. Namely, by changing the duty ratios
of the first switching element Q1 and second switching element Q2,
a voltage stored in a first current resonant capacitor Cri during
an ON period of the first switching element Q1 is adjusted, and in
an ON period of the second switching element Q2, energy accumulated
in the first current resonant capacitor Cri makes a first resonant
reactor Lr and the first current resonant capacitor Cri resonate.
As a result, a resonant current passes to transmit energy to the
secondary side, and therefore, it is possible to control the energy
to be transmitted to the secondary side. A voltage generated by a
secondary winding S1 is rectified and smoothed by a first
rectifying-smoothing circuit having a diode D1 and smoothing
capacitor C1, to output the first output voltage Vo1 from a first
output terminal.
[0173] Control of a second output voltage Vo2 will be explained. In
an ON period (time t1 to t2) of the first switching element Q1, a
differential voltage between an input voltage Vin and a terminal
voltage of the first current resonant capacitor Cri is applied to a
second series resonant circuit consisting of a second current
resonant capacitor Cri2 and the primary winding of the second
transformer T1B, so that the second series resonant circuit
conducts a resonant operation to gradually charge the second
current resonant capacitor Cri2.
[0174] In an ON period of the switching element Q2, a voltage
obtained by adding a voltage of the second resonant capacitor Cri2
to a voltage of the first resonant capacitor Cri is applied to the
primary winding of the second transformer T1B and a second resonant
reactor Lr2, the second resonant capacitor Cri2, and the first
resonant capacitor Cri produce a resonant current, which is
transmitted to the secondary side and is rectified and smoothed by
a second rectifying-smoothing circuit having a diode D2 and
smoothing capacitor C2, to output the second output voltage Vo2
from a second output terminal.
[0175] As mentioned above, the first series resonant circuit and
second series resonant circuit similarly operate in ON periods of
the switching elements Q1 and Q2. It is supposed that, for example,
the first resonant reactor Lr1 has an inductance of several .mu.H,
the second resonant reactor Lr2 has an inductance of several tens
of .mu.H, the first resonant capacitor Cri is of several hundreds
of .mu.H, and the second resonant capacitor Cri2 is of several tens
of .mu.H.
[0176] In this case, the first resonant capacitor Cri has large
capacitance to cause little voltage variation with respect to
variations in ON periods of the switching elements Q1 and Q2. In
addition, the inductance of the first resonant reactor, i.e., the
leakage inductance of the first transformer T1A is small, and
therefore, an impedance between the primary and secondary sides of
the first transformer T1A is small, so that the voltage of the
first resonant capacitor Cri multiplied by a turn ratio is provided
to the secondary side. Consequently, controlling the duties of the
switching element Q1 and switching element Q2 results in adjusting
the voltage of the first resonant capacitor Cri and controlling the
first output voltage Vo1.
[0177] On the other hand, the second resonant capacitor Cri2 has
small capacitance to cause a large voltage variation with respect
to variations in ON periods of the switching elements Q1 and Q2.
Consequently, changing a frequency corresponding to ON periods of
the switching elements Q1 and Q2 results in adjusting the amplitude
of the second resonant capacitor Cri2 and controlling the output
voltage Vo2.
[0178] Due to this, the control circuit 10a changes the ON period,
i.e., switching frequency of the second switching element Q2
according to a second voltage error signal sent from a feedback
circuit 6 and changes the ON period of the first switching element
Q1 according to a first voltage error signal sent from a feedback
circuit 5, to adjust the duties of the first switching element Q1
and second switching element Q2 and control the first output
voltage Vo1 and second output voltage Vo2 like the embodiment
1.
Embodiment 11
[0179] FIG. 27 is a circuit diagram illustrating the configuration
of a multiple output switching power source apparatus according to
the embodiment 11 of the present invention. This multiple output
switching power source apparatus is formed from the multiple output
switching power source apparatus according to the embodiment 10 of
FIG. 24 by connecting the second resonant capacitor Cri2 connected
to a connection point of the first transformer T1A and first
resonant capacitor Cri to a connection point of the second
switching element Q2 and first resonant capacitor Cri.
[0180] Operation of the multiple output switching power source
apparatus according to the embodiment 11 of the present invention
having such a configuration will be explained with reference to
waveforms illustrated in FIG. 28.
[0181] Control of a first output voltage Vo1 is carried out similar
to the multiple output switching power source apparatus of the
related art. Control of a second output voltage Vo2 will be
explained. In an ON period (time t1 to t2) of a first switching
element Q1, an input voltage Vin is applied to a second series
resonant circuit having the second current resonant capacitor Cri2
and a primary winding of a second transformer T1B, so that the
second series resonant circuit resonates to gradually charge the
second current resonant capacitor Cri2.
[0182] In an ON period of the switching element Q2, a voltage
including a voltage of the second resonant capacitor Cri2 is
applied to the primary winding of the second transformer T2B and a
second resonant reactor Lr2, the second resonant capacitor Cri2,
and the first resonant capacitor Cri produce a resonant current,
which is transmitted to the secondary side and is rectified and
smoothed by a second rectifying-smoothing circuit having a diode D2
and smoothing capacitor C2, to output the second output voltage Vo2
from a second output terminal.
[0183] As mentioned above, this embodiment differs from the
multiple output switching power source apparatus of the embodiment
10 only in the voltage applied to the second series resonant
circuit in ON periods of the switching elements Q1 and Q2 and
conducts a similar operation. Namely, this embodiment conducts
control similar to that of the embodiment 10, to control the first
output voltage Vo1 and second output voltage Vo2.
[0184] The embodiments 9 to 11 rectify and smooth a voltage
generated by the secondary winding in an ON period of the switching
element Q2, to provide the first output voltage. The same effect
will be realized by rectifying and smoothing a voltage generated by
the secondary winding in an ON period of the switching element Q1,
to provide the first output voltage.
[0185] The embodiment 11 rectifies and smoothes a voltage generated
by the secondary winding of the second transformer in an ON period
of the switching element Q2, to provide the second output voltage.
It is noted that the same effect will be realized by rectifying and
smoothing a voltage generated by the secondary winding of the
second transformer in an ON period of the switching element Q1, to
provide the second output voltage.
INDUSTRIAL APPLICABILITY
[0186] The multiple output switching power source apparatuses
according to the present invention are applicable to power source
systems for outputting a plurality of DC voltages having different
voltage values.
(The United States Designation)
[0187] In connection with designating the United States, this
application claims benefit of priority under 35USC .sctn. 119 to
Japanese Patent Applications No. 2005-289934, filed on Oct. 3,
2005, and No. 2006-044321, filed on Feb. 21, 2006, the entire
contents of which are incorporated by reference herein.
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